The present invention relates to an electric detonator having an electronic delay ignitor, and more particularly to a hybrid IC ignition circuit to be packaged in an electric detonator.
Prior art electric detonators having electronic delay ignitors are disclosed in U.S. Pat. Nos. 4,311,096, 4,445,435, 4,586,437 issued on May 6, 1986 and owned by the present assignee and Japanese Patent Application Laid-Open No. 57-142496 laid open on Sept. 3, 1982 and invented by two of the present inventors. The detonator is intended to initiate explosion of explosives such as dynamite or water gel explosive. Those are electric detonators each having an electronic ignition circuit including an energy storing capacitor, an electronic delay circuit and a switching element. The detonator is ignited by supplying a charge stored in the capacitor to a detonator ignition resistor through a switching element a predetermined time after discharging of a blasting machine.
In the detonator which uses analog delay means comprising a capacitor C and a resistor R as disclosed in U.S. Pat. 4,311,096 and Japanese Patent Application Laid-Open No. 57-142496, a timing precision is significantly influenced by an applied voltage, a temperature change and variance in individual components and hence it has a problem in practical use. The timing precision or delay accuracy of such detonator is not much different than that of a prior art delay powder type electric detonator.
When the analog delay switching circuit having a capacitor (C) 9 and a resistor (R) 8 shown in FIG. 6 is implemented by a monolithic IC, it is difficult in manufacture to integrate a switching thyristor (SCR) 19 and a PUT (programmable unijunction transistor) 18 having reference voltage resistors 5 and 6 connected thereto into the monolithic IC. Even if they are integrated, a power supply capacitor 7 must be large because of an insufficient delay accuracy and a large current consumption. Accordingly, it is not appropriate to the IC delay element of the electric detonator.
In addition, since the electronic delay detonator contains the energy storing power supply capacitor 7, if input terminals 10 and 11 are opened, an external stray current is gradually stored in the energy storing power supply capacitor 7 through an input line.
As the amount of stored charge increases, the stored charge activates the delay switching circuit so that a trigger signal is applied to the switching element 19 such as a thyristor and the ignition charge stored in the capacitor 7 flows into an ignition resistor wire 16 through the switching element 19 to heat the resistor wire 16. As a result, the detonator is ignited inadvertently.
The amount of stored charge depends on whether the stray current is pulsive (single pulse or repetitive pulse) or continuous. When the stray current is continuous, the electronic delay detonator is fired in several seconds to several tens of seconds when the stray current is approximately 2 mA at 10 volts. Further, in those electronic delay detonators, inconveniently it is not possible to check and measure continuity and series-connection resistance. The problems in the stray current and continuity check of the detonator also apply to a detonator with digital delay means to be described below.
The detonator having digital delay means as disclosed in U.S. Pat. Nos. 4,445,435 and 4,586,437 has a more accurate timing precision than that of the analog delay switching circuit but it is not practical to use in a disposable detonator because it must use an expensive quartz resonator or ceramic resonator. If a relatively inexpensive CR oscillator is used, an oscillation IC and a counter IC are required and a separate current switching element (for example SCR) must be provided. As a result, it is difficult to integrate those elements in one chip and size reduction is restricted.